diff --git a/dash/backends/_fastapi.py b/dash/backends/_fastapi.py
index 0b27f43692..867e9a25b0 100644
--- a/dash/backends/_fastapi.py
+++ b/dash/backends/_fastapi.py
@@ -28,10 +28,11 @@
     ) from _err
 
 from dash.fingerprint import check_fingerprint
-from dash import _validate
+from dash import _validate, get_app
 from dash.exceptions import PreventUpdate
 from .base_server import BaseDashServer, RequestAdapter, ResponseAdapter
 from ._utils import format_traceback_html
+import traceback
 
 if TYPE_CHECKING:  # pragma: no cover - typing only
     from dash import Dash
@@ -122,8 +123,12 @@ async def _initialize_dev_tools(self) -> None:
                 self.dash_app.enable_dev_tools(**config, first_run=False)
             self._dev_tools_initialized = True
 
-    def _setup_timing(self, request: Request) -> None:
+    async def _setup_timing(self, request: Request) -> None:
         """Set up timing information for the request."""
+        try:
+            request.state.json_body = await request.json() if request.headers.get("content-type", "").startswith("application/json") else None
+        except:
+            request.state.json_body = None
         if self.enable_timing:
             request.state.timing_information = {
                 "__dash_server": {"dur": time.time(), "desc": None}
@@ -179,6 +184,12 @@ async def _handle_error(
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         # Handle lifespan events (startup/shutdown)
         if scope["type"] == "lifespan":
+            try:
+                dash_app = get_app()
+                dash_app.backend._setup_catchall()
+            except:
+                print("Error during catch-all setup:")
+                print(traceback.format_exc())
             await self._initialize_dev_tools()
             await self.app(scope, receive, send)
             return
@@ -193,7 +204,7 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         token = set_current_request(request)
 
         try:
-            self._setup_timing(request)
+            await self._setup_timing(request)
             await self._run_before_hooks()
 
             await self.app(scope, receive, send)
@@ -275,11 +286,24 @@ async def index(_request: Request):
         dash_app._add_url("", index, methods=["GET"])
 
     def setup_catchall(self, dash_app: Dash):
-        async def catchall(_request: Request):
-            return Response(content=dash_app.index(), media_type="text/html")
+        '''This is needed to ensure that all routes are handled by FastAPI
+        and passed through the middleware, which is necessary for features like authentication
+        and timing to work correctly on all routes. FastAPI will match this catch-all route
+        for any path that isn't matched by a more specific route, allowing the middleware to
+        process the request and then return the appropriate response (e.g., 404 if no Dash route matches).'''
 
-        # pylint: disable=protected-access
-        dash_app._add_url("{path:path}", catchall, methods=["GET"])
+
+    def _setup_catchall(self):
+        try:
+            print("Setting up catch-all route for unmatched paths")
+            dash_app = get_app()
+            async def catchall(_request: Request):
+                return Response(content=dash_app.index(), media_type="text/html")
+
+            # pylint: disable=protected-access
+            self.add_url_rule("{path:path}", catchall, methods=["GET"])
+        except:
+            print(traceback.format_exc())
 
     def add_url_rule(
         self,
@@ -289,6 +313,7 @@ def add_url_rule(
         methods: list[str] | None = None,
         include_in_schema: bool = False,
     ):
+        print(f"Adding URL rule: {rule} -> {view_func} (endpoint: {endpoint}, methods: {methods})")
         if rule == "":
             rule = "/"
         if isinstance(view_func, str):
@@ -481,7 +506,7 @@ def add_redirect_rule(self, app, fullname, path):
     def serve_callback(self, dash_app: Dash):
         async def _dispatch(request: Request):
             # pylint: disable=protected-access
-            body = await request.json()
+            body = self.request_adapter().get_json()
             cb_ctx = dash_app._initialize_context(
                 body
             )  # pylint: disable=protected-access
@@ -641,5 +666,13 @@ def origin(self):
     def path(self):
         return self._request.url.path
 
+    async def _get_json(self, request: Request=None):
+        req = self._request
+        if not hasattr(req.state, "json_body"):
+            req.state.json_body = await request.json()
+        return req.state.json_body
+
     def get_json(self):
-        return asyncio.run(self._request.json())
+        if not hasattr(self, "_request") or self._request is None:
+            self._request = get_current_request()
+        return self._request.state.json_body